1. Field of the Invention
This invention relates to slip joints for use in well strings, and more particularly, to a slip joint utilizing round mandrels and having removable key and bearing means.
2. Description of the Prior Art
Offshore wells with floating platforms present a problem in compensating for vertical movement of the platform. Without compensation, such vertical movement would transmit undesirable axial loads on a rigid well string extending downwardly from the platform. The solution has been to place at least one slip joint in the well string which compensates for the movement of the platform by axial telescoping action. A further problem is that such a slip joint must also be capable of transmitting torque so that a portion of the well string below the slip joint will be rotated concurrently with a portion of the well string above the slip joint.
A telescoping slip joint commonly used is of the type disclosed in U.S. Pat. No. 3,354,950 to Hyde. In the first embodiment disclosed in Hyde, an inner mandrel moves telescopingly within an outer mandrel. The inner mandrel defines a polygonal portion which extends into a corresponding polygonally shaped opening in the outer mandrel. The interaction of the polygonal surfaces provides a means for transmitting torque therebetween. It is necessary to seal between the mandrels so that fluid outside of the slip joint is not in communication with fluid passing through the well string. The problem with a slip joint using the polygonal configuration of Hyde is that the polygonal portion must be totally exposed or some method of sealing along the polygonal surface must be provided. Also, the polygonal portions are difficult and expensive to manufacture, and the entire apparatus must be dismantled for repair.
One solution to this problem is to provide a mandrel with only round surfaces, and one such slip joint is shown in an alternate embodiment in Hyde. However, even in the alternate embodiment of Hyde, which uses a key in a longitudinal keyway for transmitting torque, the key is not removable and major portions of the slip joint have to be replaced when repair becomes necessary.
The slip joint of the present invention solves these problems by having easily replaceable key means therein.
Another problem with slip joints of the prior art is that there is a possibility of radial loading on the sealing members therein which results in early failure. Also, internal parts are more likely to contact one another and wear in such a situation. The preferred embodiment of the present invention solves this problem by providing bearing means for precise location of the inner mandrel and for mutual guidance between the mandrels during relative axial motion thereof.